This invention relates to antifriction roller bearing assemblies, and relates more particularly to improvements therein preventing roller end wear.
Antifriction bearing assemblies generally comprise inner and outer circular races between which are disposed a plurality of roller bearing members in rolling engagement with the inner and outer races. Conventionally, end flanges are included in one or both of the inner and outer races, and the end faces of the bearing members are engagable with these end flanges. This engagement has drastically limited the life, and predictability of life, of prior art antifriction roller bearing assemblies. Manufacturing tolerances ultimately cause the roller bearings to become sufficiently skewed within the raceway of the inner and outer races such that line to line contact ultimately occurs between the end face of the roller bearing and the upper corner of the race end flange. Occurrence of this line to line contact varies relative to the manufacturing tolerances involved, thus leading to unpredictability of roller bearing life. This problem is particularly deleterious in extremely high speed roller bearing applications such as the roller bearings utilized on mainshafts in gas turbine engines.
While various arrangements have been contemplated to reduce roller bearing end wear, such as crowned roller bearing ends, and/or tapered race end flanges, the problems of roller bearing end wear and resultant unpredictability in roller bearing life still is prevalent particularly with respect to high speed applications.
More particularly, the primary failure in cylindrical roller bearings used in high speed applications is induced by the roller bearing end wear. Such wear causes the loss of control of the roller bearing, fatigue loading of the separator utilized to separate adjacent roller bearings, fracture of the separator, magnified skidding of the roller upon the race and subsequent complete bearing failure.
Roller end wear occurs primarily whenever the roller end contacts the guide flange of the race under conditions where the oil film thickness is less than that required to separate the surface asperities. The wear is especially severe if the roller end contacts the top or outer corner of the flange to wipe the oil film from the roller end and further promote metal-to-metal contact. The wear rate increases further if the corner of the end of the roller contacts the outer corner of the race end flange. This corner-to-corner contact is prevalent to one extent or another in substantially all roller bearings manufactured today. Such roller end wear is relatively random in nature as it depends on blend radii and wear-in that affect skewing torques exerted upon the roller bearing. Roller skewing moments are essentially a result of imperfect and imprecise manufacturing, as well as the necessary manufacturing tolerances. The flange end and roller end must be capable of reacting and withstanding the maximum roller skewing moment which occurs when the roller skewing absorbs all of the end clearance between the roller and the guide flanges of the race. Exemplary of those manufacturing tolerances which assist in producing roller skewing moments include raceway taper, roller cylindrical surface taper, roller crowning variations, and off-square roller ends.
Prior attempts to achieve and improve lubrication between the roller end and the race guide flange in high speed cylindrical roller bearing designs incorporate various arrangements which are difficult and expensive to control and do not successfully obtain the desired results. Such prior art arrangements include blending of surfaces at the intersections of the corner of the end of the roller bearing, as well as blending of surfaces at the outer corner of the race guide flange, centrifugally fed lubrication ports in the raceway itself adjacent the base of the race end flanges, and dynamic mass balancing of each individual roller. As a practical matter, such arrangements are not consistently attainable, are relatively extremely expensive, and still result in unreliable bearing installation in spite of high bearing cost.